Bus passengers caught up in a terror alert caused by an electronic cigarette have told how they feared for their lives.

The M6 toll road near Lichfield was closed in both directions for more than four hours as armed officers, troops, firefighters and bomb disposal experts all raced to the scene after a passenger reported seeing vapour coming from a man's bag.

A decontamination unit was set up and passengers were searched and held in a makeshift pen on the carriageway, but police found no crime had been committed. The man was simply using an electronic cigarette, rather than the real thing, on the six-hour journey from Preston to London.

After finally arriving at Victoria Coach Station on a replacement bus, student Vermilion Von Kangur, 20, told of how she had feared for her life as armed police swooped around the coach.

She said: "Some people thought there was a bomb on the bus, some people thought it was going to explode. Some people thought the bus had broken down, or that there was a prisoner on board. I was scared."

She said everyone on board was made to leave it one by one at 10-minute intervals with their hands clearly visible, as officers looked on with their guns poised.

Military personnel, police dog handlers, firefighters and other specialist units were also sent to the scene after police received a report from "a genuinely concerned member of the public" at about 8.20am on Thursday. They said they had seen vapour coming out of the bag as the coach was near the M6 toll plaza at Weeford, near Lichfield.

Officers responded "swiftly and proportionately" to "a genuine report from a member of the public", a Staffordshire Police spokeswoman said. "The information received concerned a report of vapour escaping from a bag which on investigation turned out to be a health improvement aid for smokers."

With the Olympic Games, considered an attractive target for potential terrorists, starting later this month, police have urged the public to remain vigilant and report any suspicious activity. Police later confirmed the device was an electronic cigarette which gives off a visible vapour.

A spokeswoman for Megabus, which is operated by Stagecoach, said 48 passengers were booked on the 5.10am Preston to London service and all were safe and well.